Spring piston return



April 14, 1970 .J. BRUNELLE 3,506,178

SPRING PISTON RETURN Filed Dec. 14, 1967 2 Sheets-Sheet 1 L INVENTOR" J H LAWRENCE J. BRUNELLE l I By ATTORNEY Apri 1 1970 L. J. BRU ELLE 3,50 11 SPRING PI STON RETURN Filed Dec. 14, 1967 2 Sheets-Sheet 2 INVENTOR LA WRg/VCE J BRUNELLE BY M ATTORNEY United States Patent 3,506,178 SPRING PISTON RETURN Lawrence J. Brunelle, East Haven, Conn., assignor to Olin Mathieson Chemical Corporation, a corporation of Virginia Filed Dec. 14, 1967, Ser. No. 690,437 Int. Cl. B25c 1/14, /02 US. Cl. 227- 23 Claims ABSTRACT OF THE DISCLOSURE A power actuated piston tool in which a spring-biased lever is operative to return the piston from its driven position to its firing position.

This invention relates to a power actuated piston tool, and more particularly to a spring-type piston return system for use with a power actuated tool.

Power actuated piston-type tools have, in recent years achieved great commercial success in the construction and related fields. The power actuated piston tools of the prior art may utilize piston velocities of from 250 to 300 feet per second when the piston is. moved from the firing position to the driven position to set a fastener into a surface, and piston velocitie of this magnitude have created problems with respect to providing a dependable automatic system whereby the piston is returned from the driven position to the firing position. As a result, the majority of the piston-type power tools include manually operable means to return the piston from the driven position to the firing position, one such means being disclosed in US. Patent No. 3,066,302. While such manually operable means has proven generally satisfactory, in order to expedite operation of the tool, an automatic piston return system is highly desirable.

One solution to an automatic piston return would appear to lie in the provision of a metallic spring means disposed within the barrel, bearing against the piston, whereby movement of the piston from the firing position to the driven position would compress the spring to store energy therein. After a fastener is driven by the piston, the spring would then theoretically return to its original configuration returning the piston to the firing position. Experimentation has, however, proven that a metallic spring will set, that is to say, will become incapable of returning to its original configuration and will be permanently deformed as a result of shock waves induced therein, when the spring is subjected to a piston moving at a velocity in the range of 250-300 feet per second, and indeed setting of the spring will occur at piston velocities in excess of about 50 per second.

The power actuated tool and piston return system of this invention include a housing having a barrel connected thereto. A piston is disposed within the barrel for reciprocating movement between a firing position and a driven position. A firing chamber is disposed adjacent to the barrel and in communication therewith and firing means are disposed within the housing operable to detonate a charge in the firing chamber, the detonation supplying energy to drive the piston from the firing position to the driven position. Piston return means are provided to return the piston firom the driven position to the firing position, which piston return means includes a lever which is pivotally mounted on the housing so that the lever is generally transverses to the axis of the piston. A free end of the lever engages the piston, with the pivotal axis of the lever being spaced apart from the piston a predetermined distance. Spring means are mounted on the housing in engagement with the lever at a point which is spaced apart from the pivotal axis a predetermined distance and which is also spaced apart from the piston. The spring means serves the bias the free end of the lever and thereby bias the piston toward the firing position.

It is, therefore, an object of this invention to provide a power actuated tool having an automatic piston return system utilizing spring-biased lever means.

It is a further object of this invention to provide an automatic piston return system which may be used in conjunction with a power actuated tool having a piston velocity in the order of 250300 feet per second.

It is a still further object of this invention to provide a power actuated tool having an automatic piston return system which utilizes a metallic spring, wherein the spring is not exposed to the full piston velocitywhen the piston is moved through its work stroke.

It is yet another object of this invention to provide an automatic piston return system for use with a piston-type power actuated tool which return system is durable and dependable over extended periods of usage.

Other features, objects and advantages of the invention will become apparent from the following detailed description and accompanying drawings in which:

FIGURE 1 is a side view, partially in section, of the piston-type power actuated tool of this invention with the piston shown in the firing position;

FIGURE 2 is a side view, partially in section, of the tool of FIGURE 1 wherein the piston is in the driven position;

FIGURE 3 is a top sectional view taken along line 3-3 of FIGURE 2; and

FIGURE 4 is a fragmentary side view of a modified embodiment disclosing an alternative placement of a buffer which may be used with the invention.

Referring more particularly to FIGURE 1, a pistontype power actuated tool is disclosed which includes a housing indicated generally by the numeral 2. The housing 2 has a top portion 4 and a bottom portion 6 which are hingedly joined together by a laterally extending pin 8. The bottom portion 6 of the housing 2 includes a base 10 extending the length thereof which base 10 has a threaded aperture 12 adjacent one end. A barrel 14, having a threaded portion 16 which is screwed into the aperture 12, is mounted on the base 10, and a piston, indicated generally by the numberal 18, is disposed in the barrel 14 for reciprocal movement therein. The piston 18 includes an enlarged head portion 20 and a stern portion 22. A firing chamber 24 is disposed adjacent to the barrel 14 in communication therewith, the firing chamber 24 being for the reception of a charge 26 in the form of a cartridge or the like.

The upper portion 4 of the housing 2 includes a thickened wall part 28 which is ordinarily disposed against the outer face of the wall of the firing chamber 24 and which is removably locked thereagainst by a plurality of flexible fingers 30 having head portions 32 biased into engagement with notches 34 in the side of the wall part 28. The wall part 38 includes an aperture 36 disposed in alignment with the charge 26. The upper portion 4 of the housing 2 further includes an aperture 38 which is substantially coaxial with the aperture 36. A firing pin assembly is movably mounted in the upper portion 4 of the housing 2, the firing pin assembly, including a first segment 40 extending into and movably within the aperture 36 and a second segment 42 extending through and movable within the aperture 38. The firing pin assembly further includes a flange 44 interposed between the segments 40 and 42. A compressible spring 46 is mounted on the upper portion 4 of the housing 2 and engages the flange 44 to bias the firing pin assembly toward the charge 26. A disk-shaped member 48 is disposed on the outer end of the second segment 42 to provide means whereby the firing pin assembly can be manually moved against the bias of the spring 46.

A sear pin 50 is movably mounted in an aperture 52 and a compressible spring 54 is disposed in the bottom of the aperture 52 to bias the sear pin 50 toward the first segment 40 of the firing pin assembly. The forward end of the sear pin 50 includes a protuberance 58 for engagement with a notch 56 on the first segment 40 of the firing pin assembly. Trigger means 60 is mounted on the upper portion 4 of the housing 2 for pivotal movement about a pin 62, the trigger means 60 projecting into a hand grip aperture 64 which forms a handle in the upper portion 4 of the housing 2. A lug 66 is provided to limit the pivotal movement of the trigger 60 in one direction. A sear actuator 68 is mounted on the upper portion 4 of the housing 2 to pivot about a pin 7 one end of the sear actuator 68 engaging a notch 72 in the sear pin 50 and the other end of the sear actuator 68 engaging the trigger 60.

The trigger and firing pin assembly, thus described, operate in the following manner to detonate a charge. The upper portion 4 of the housing 2 is pivoted about the pin 8 (to the position shown in phantom in FIGURE 1) to open the firing chamber 24, and a charge 26 is placed therein. The upper portion 4 is then pivoted back until the fingers 30 engage the notches 34 to lock the wall portion 28 against the firing chamber wall. The disk 48 is then grasped and the firing pin assembly is manually pulled against the bias of the spring 46 until the protuberance 58 on the sear pin 50 enters the notch 56, with the sear pin 50 moving to the left under the influence of the spring 54. The firing pin assembly is then in a cocked position as shown in FIGURE 1. The trigger 60 is then pulled to pivot in a counter-clockwise direction about the pin 62, which pivotal movement of the trigger 60 causes) the sear actuator 68 to pivot in a clockwise direction about the pin 70. The clockwise pivotal movement of the sear actuator 68 causes the sear pin 50 to move to the right against the bias of the spring 54 thereby moving the protuberance 58 out of the notch 56. The spring 46 then moves the firing pin assembly toward the charge 26 and upon impact the latter is detonated. The position of the various elements after detonation is shown in FIGURE 2.

The piston return means of this invention includes a lever 74 which is mounted on the lower portion 6 of the housing 2 for pivotal movement about a pin 76, which pin is spaced apart from the axis of the piston 18. One end portion of the lever 74 is bifurcated to form prongs 78 and 80, mostly clearly shown in FIGURE 3, the bifurcated end portion of the lever 74 extending through a slot 82 which is formed in the wall of the barrel 14. A compressible spring 84 is mounted on the base and engages the lever 74 at a point which is spaced apart from the pivot pin 76 and which is also spaced apart from the axis of the piston 18. The spring 84 biases the bifurcated end of the lever 78 upward into engagement with the head of the piston 18. A pair of oppositely disposed nubs 86 and 88 are preferably disposed respectively on the base 10 and on the lever 74 to engage the opposite ends of the spring 84. A buffering block 90 of shock-absorbing material, such as polyurethane, nylon, or the like, is disposed on the base 10 adjacent to the barrel 14, the buffering block 90 extending upwardly beyond the lower edge of the slot 82.

FIGURE 4 disclosed an alternative arrangement of parts for providing a buffering block, wherein the buffering element is in the form of an annular body 96 of polyurethane, nylon, or the like which is disposed within the lower portion of the barrel 14 and seated against an inwardly extending flange 94 at the lower end of the barrel. An annular plug 92 is disposed above the buffering element 96 to transfer impact energy from the lever 74 to the buffering element 96.

A fastener magazine 98 containing a plurality of fasteners 100 is mounted on the bottom of the base 10 in any known manner, the magazine 98 having means (not shown) for automatically advancing individual fasteners 100 to a driving position beneath the piston stem 22. A pair of coaxial apertures 102 and 104 are disposed in the top and bottom respectively of the magazine 98 to permit passage of the piston stem 22 through the magazine 98 to drive a fastener 100 (see FIGURE 2). A flexible blade spring 106 is disposed at the apertured end of the magazine 98 to aid in aligning the fastener 100 prior to driving the latter into a surface 108.

The power actuated tool and the piston return system of this invention operate in the following manner. The piston 18 is held in the firing position, as shown in FIG- URE 1, by the prongs 78 and of the lever 74 which are biased upwardly against the piston head 30 by the spring 84.

The piston 18 is moved to the driven position shown in FIGURE 2 by detonating a charge 26 in the firing chamber 24, there being a plurality of apertures 110 in the wall of the barrel 14 to vent the latter after detonation. Movement of the piston 18 to the driven position causes the lever 74 to pivot to the position shown in FIGURE 2 and results in compression of the spring 84. Impact of the lever 74 with the buffer pad results in dissipation of energy developed by the moving piston 18 and lever 74, and provides a safeguard in the event of free firing or overfiring of the piston 18.

The velocity of that point on the lever acting on the spring 84 during movement of the piston 18 from the firing position to the driven position is determined by the formula V /V =d /d where: V is the piston velocity in feet per second; V is the velocity in feet per second of the lever at the point of engagement of the lever and the spring; d is the distance in inches between the axis of the piston and the pivotal axis of the lever; and d is the distance in inches between the point of engagement of the lever and the spring, and the pivotal axis of the lever. Thus the velocity of that point on the lever acting upon the spring 84 is directly proportional to d for a given V and d Once the setting lever velocity for a particular spring composition is experimentally determined, control of V is achieved by properly establishing d with the result that the spring is never exposed to a lever velocity that will cause it to set.

After the fastener has been driven by the piston 18, the lever 74 must exert a sufficient force on the piston 18 to return the latter to the firing position. Ordinarily 1-2 pounds will be sufficient, depending on the weight and friction of the piston 18 and the weight of the lever 74. Since the spring 84 is laterally offset from the piston 18, the spring 84 must exert a force against the lever 74, which is greater than the piston return force. The necessary spring force may be determined by the formula f =f (d -d where; f is the spring force; f is the piston return force; and d and d are as defined above.

This invention thus provides a power actuated piston tool having an automatic spring-biased piston return system. The tool of this invention obviates the need of manually resetting the piston after each shot and provides an arrangement of parts wherein the spring is not subjected to the pull piston velocity during firing of the tool. The invention further provides a tool which may readily be associated with a fastener magazine which automatically advances fasteners to a driving position beneath the piston thus greatly accelerating the rate at which the tool may be used and simplifying procedures involved in driving a power-set fastener.

Although reference has been made to a particular embodiment of the present invention, various modifications will readily suggest themselves to those skilled in the art and reference should be made to the appended claims to determine the scope of the invention.

What is claimed is:

1. A piston return system comprising:

(a) a barrel;

(b) a piston mounted in said barrel and movable therein between a firing position and a driven position at a velocity from said firing position to said driven position of at least about 50 feet per second;

(c) a rigid lever having a free end for engagement with said piston;

(d) means connected to said barrel for mounting said lever for pivotal movement about an axis, said pivotal axis being spaced apart from said piston; and

(e) coil spring means engaging said lever at a point spaced apart from said pivotal axis and from said piston to bias said free end of said lever and thereby bias said piston toward said firing position.

2. The piston return system of claim 1, wherein said barrel includes a slot in its wall for the passage of said free end of said lever to engage said piston.

3. The piston return system of claim 2, wherein said piston includes a stem portion and an enlarged head portion, and wherein said free end of said lever is bifurcated to define prongs for engagement with said piston head.

4. A piston-type power actuated tool comprising:

(a) a housing;

(b) a barrel connected to said housing;

(c) a piston mounted in said barrel for reciprocating movement therein between a firing position and a driven position;

(d) a rigid lever having a free end for engaging said piston, said lever being connected to said housing for pivotal movement about an axis which is spaced apart from said piston; and

(e) coil spring means connected to said housing and engaging said lever at a point spaced apart from said piston and from said pivotal axis to bias said free end of said lever and thereby bias said piston toward said firing position.

5. The power actuated tool of claim 4, wherein said barrel has a slot in its wall for the passage of said free end of said lever to engage said piston.

6. The power actuated tool of claim 5, wherein said piston includes a stem portion and an enlarged head portion, and wherein said free end of said lever is bifurcated to define prongs for engagement with said piston head.

7. The power actuated tool of claim 4, wherein bufier means is connected to said housing to engage said lever when said piston is in the driven position.

8. The power actuated tool of claim 7, wherein said buffer means is disposed in said barrel.

9. The power actuated tool of claim 7, wherein said buffer means is composed of polyurethane.

10. The power actuated tool of claim 8, wherein said buffer means is composed of polyurethane.

11. A piston-type power actuated tool comprising:

(a) a housing;

(b) a barrel connected to said housing;

(c) a piston mounted in said barrel for reciprocating movement therein between a firing position and a driven position;

(d) a firing chamber in said housing and in communication with said barrel;

(e) a lever having a free end for engaging said piston,

said lever being connected to said housing for pivotal movement about an axis which is spaced apart from said piston;

(f) spring means connected to said housing and engaging said lever at a point spaced apart from said pivotal axis and from said piston to bias said free end of said lever and thereby bias said piston toward said firing position; and

(g) [means connected to said housing operable to detonate a charge in said firing chamber to move said piston from said firing position to said driven position.

12. The power actuated tool of claim 11, wherein said barrel has a slot in its wall for the passage of said free end of said lever to engage said piston.

13. The power actuated tool of claim 12, wherein said piston includes a stem portion and an enlarged head portion, and wherein said free end of said lever is bifurcated to define prongs for engagement with said piston head.

14. The power actuated tool of claim 11, wherein buffer means is connected to said housing to engage said lever when said piston is in said driven position.

15. The power actuated tool of claim 14, wherein said buffer means is disposed in said barrel.

1 6. The power actuated tool of claim 14, wherein said bufier means is composed of polyurethane.

17. The power actuated tool of claim 15, wherein said buffer means is composed of polyurethane.

18. A piston-type power actuated tool comprising:

(a) an elongated substantially rectangular housing having a lower portion, and having an upper portion hingedly afiixed to said lower portion;

(b) handle means on said upper portion;

(0) releasable latching means to restrain said upper portion against pivotal movement with respect to said lower portion;

((1) a barrel attached to said lower portion adjacent one end thereof, said barrel having a slot in its wall;

(e) a piston having a stem and an enlarged head mounted in said barrel for reciprocal movement therein between a firing position and a driven position;

(f) a lever extending generally transversely to said piston, said lever being connected to said lower portion for pivotal movement about an axis which is spaced apart from said piston, and said lever extend ing through said barrel slot and having a bifurcated free end for engagement with said piston head;

(g) spring means connected to said lower portion, said spring means engaging said lever at a point which is spaced apart from said pivotal axis and which is spaced apart from said piston to bias said free end of said lever and thereby bias said piston toward said firing position;

(h) a firing chamber adjacent to said barrel and in communication therewith; and

(i) means disposed on said housing operable to detonate a charge in said firing chamber to move said piston from said firing position to said driven position.

19. The power actuated tool of claim 18, wherein butler means is connected to said lower portion to engage said lever when said piston is in said driven position.

20. The power actuated tool of claim 19, wherein said buffer means is disposed in said barrel.

21. The power actuated tool of claim 19, wherein said buffer means is composed of polyurethane.

22. The power actuated tool of claim 20, wherein said buffer means is composed of polyurethane.

23. The power actuated tool of claim 18, wherein a fastener magazine is attached to said lower portion to automatically sequentially feed individual ones of a plurality of fasteners disposed in said magazine to a position adjacent to one end of said barrel prior to driving the fasteners into a surface.

References Cited UNITED STATES PATENTS 2,632,890 3/1953 Tietig 227-10 3,017,636 1/ 1962 Koennicke 227 -134 XR 3,331,546 7/ 1967 Brunelle 227l0 GRANVILLE Y. CUSTER, JR., Primary Examiner US. Cl. X.R. 227134 

